class A{
    n="A";
    fun(){
        console.log(this.constructor.name);
        for(let key in this){
            console.log(key+"="+this[key]);
        }
    }
}



class B extends A{
    age=20;
    nul;
}
var a = new A();
a.fun();
var b = new B();
b.fun();
console.log(b["c"]);


console.log(JSON.stringify(b));

